This study aimed to screen for Lewis antigens in Thai newborns. Although, these antigens are known to be weak or absent on the red cells of newborns, we encountered a case of a Le(a+) newborn baby when testing with monoclonal antibody and human anti-Le(a). Such a finding led us to conduct this study to explore further evidence of Lewis antigens in Thai newborn red cells. A total of 197 cord blood samples were tested with monoclonal anti-Le(a) and anti-Le(b). (Bioclone, Ortho Diagnostic Systems, USA). The tests were performed according to the manufacturer's recommendations. The results revealed that none of the cord red cells in this study group possessed Lewis antigens. This study showed that Lewis antigens were absent or were so extremely weak on the red cells of these newborn infants that they could not be demonstrated despite the use of potent monoclonal antibodies. However, further study should be done by using more cord blood samples, a more sensitive technique or even more potent antisera.